From the Guidelines
Ionized calcium is the biologically active form of calcium in the blood, typically making up about 50% of the total calcium, and its normal levels range from approximately 4.5 to 5.1 mg/dL (1.1 to 1.3 mmol/L) 1. When considering the management of ionized calcium levels, it's essential to prioritize the prevention of hypercalcemia, especially in patients with chronic kidney disease (CKD) stages G3a to G5D, as higher calcium concentrations have been linked to increased mortality and nonfatal cardiovascular events 1.
Key Considerations
- Ionized calcium is crucial for various bodily functions, including muscle contraction, nerve transmission, and hormone secretion.
- Measuring ionized calcium provides a more accurate assessment of calcium status than total calcium, particularly in patients with abnormal protein levels or acid-base disturbances 1.
- Conditions that affect protein levels or blood pH can alter the binding of calcium to proteins without changing the amount of ionized calcium.
- Ionized calcium values are not significantly affected by changes in albumin levels, making them valuable in clinical situations where protein levels may be abnormal.
Clinical Implications
- Doctors often order ionized calcium tests when investigating parathyroid disorders, kidney disease, certain cancers, or when managing critically ill patients.
- The prevention of hypercalcemia is crucial, and treatment should focus on patients with hyperphosphatemia, especially in those with CKD stages G3a to G5D 1.
- The use of a dialysate calcium concentration between 1.25 and 1.50 mmol/L (2.5 and 3.0 mEq/L) is recommended for patients with CKD stage G5D 1.
From the FDA Drug Label
Ionized calcium and gluconate are normal constituents of body fluids. About 50% of total serum calcium is in the ionized form and represents the biologically active part.
Ionized calcium is the biologically active part of calcium in the body, representing about 50% of total serum calcium. It is a normal constituent of body fluids and plays a crucial role in various bodily functions.
- Ionized calcium is the form of calcium that is directly available for physiological use.
- The remaining serum calcium is bound to organic and inorganic acids or proteins, such as albumin 2.
From the Research
Definition of Ionized Calcium
- Ionized calcium is the biologically active form of calcium in the extracellular fluid 3
- It is the concentration of ionized calcium that is biologically active, not the albumin-corrected calcium 4
Measurement of Ionized Calcium
- Ionized calcium is measured in blood samples, and its concentration can be affected by pH levels 4
- Samples are typically analyzed at the actual pH of the individual patient to ensure accurate results 4
Clinical Significance of Ionized Calcium
- Ionized calcium plays a crucial role in the diagnosis and treatment of secondary hyperparathyroidism in patients with chronic renal failure 4, 5, 6
- The use of ionized calcium rather than albumin-corrected calcium can influence the calcium classification of individual patients and have clinical implications for treatment 4
Relationship between Ionized Calcium and Other Parameters
- Ionized calcium is related to other parameters such as parathyroid hormone (PTH), calcium x phosphorus product, and intact parathyroid hormone 4, 5, 6
- The measurement of ionized calcium and cyclic AMP in plasma and urine can be used to evaluate calcium disorders and detect primary and secondary hyperparathyroidism 3